Vortex baffle

ABSTRACT

Spin stabilized rocket motor with end burning solid propellant grain in which cratering of the grain is eliminated by channeling gaseous products of combustion through angularly spaced apertures disposed outwardly from the rocket axis and thence radially inwardly to an axially disposed exhaust nozzle.

United States Patent [191 Thorsted et a]. 1 Jan. 23, 1973 [5 1 VORTEX BAFFLE 676,368 7/1952 Great Britain ..60/253 [75] Inventors: Kenneth G. Thorsted; Robert Primary Examiner samuelFeinberg Dillinger, both of China Lake, Callf. AttorneyG. J. Rubens, R. Miller, V. C. Muller and [73] Assignee: The United States of America as 'Q represented by the Secretary of the Navy 221 Filed: Nov. 2, 1966 [57] ABSTRACT Spin stabilized rocket motor with end burning solid [2]] ApplNo': 593260 propellant grain in which cratering of the grain is 521 05.0 ..60/253, 244/123 eliminated by channe'ing gasews pmducs [51] Fozk 9/04 bustion through angularly spaced apertures disposed l f outwardly from the rocket axis and thence radially in- Fle d 0 Search wardly to an axially disposed exhaust nozzle' References Cited 2 Claims, 3 Drawing Figures FOREIGN PATENTS OR APPLICATIONS 6/1946 Great Britain ..60/253 PATENIEU P4235975 a if 1 2 O61 Fl G. 3. INVENTORS. KENNETH 6. TH STED ROBERT E. DIL GER BY v. c. MULLER ROY MILLER ATTORNEYS.

VORTEX BAFFLE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to spin stabilized rocket motors and more particularly to improvements in motors of such type which employ solid cylindrical end burning grains.

In the testing of rocket motors employing solid end burning grains which exhaust through a central axial nozzle, certain phenomenon has been observed by varying the spin speed, measuring the thrust and recording the burning characteristics of the burning grain by X-ray techniques. Spin speeds were varied between and 200 revolutions per second with grains of the order of 4 inches in diameter. The time-thrust traces showed that when the motor was static or rotated at relatively low spin speeds the thrust quickly rose to maximum, remained at a plateau, and then quickly dropped toward the end of burning. As spin speed was increased beyond the order of 100 rps and up to 200 rps, the thrust continued to increase to a maximum peak beyond the former plateau and then decreased which indicated that a progressive burning was taking place, the progressivity and peak thrust increasing with increase in spin speed. When the actual burning configuration was observed by X-ray techniques it was found that a cone shaped cavity was formed at the center of the grain. It was theorized that the coning was caused by a vortex action of the exhaust gases since the gases evolving from the end of the grain should be rotating at essentially the same velocity of the grain and that to conserve angular momentum as they approach the motor center line to exhaust through the central nozzle they must necessarily increase in angular velocity. This led to the further hypothesis that the gas at the center of the motor was producing an erosive type of burning causing the coning of the grain. This theory was supported by an unintended experiment, where the motor failed before burnout, and the conical cavity was eroded in spiral channels between the conical cavity and outer radial portions of the grain. It was reasoned that if the vortex theory was correct the coning erosion should decrease if the gases were exhausted through openings disposed at points radially outwardly from the center of the motor. Tests with two diametrically opposed openings about midway between the motor axis and grain periphery revealed reduced progressively of burning (flattened peak thrust) and the substitution of two craters, aligned with the openings, these being of reduced magnitude of the single crater or cone encountered with a single nozzle. The substitution, next, of a baffle plate having six equiangularly spaced radial vanes on its front face, covered by a front flat plate, which caused the gases to exhaust into the outer ends of the spaces formed by the baffle plate and cover plate and thence inwardly to an axial exhaust port eliminated the central coning and produced plateau burning without peak thrust formerly encountered. As will now be apparent, the present invention burns substantially uniformly and produces substantially uniform thrust throughout the major portion of its consumption.

Another object is to provide a baffle or other gas communication channeling which will reduce the detrimental vortex action of gases within a combustion chamber in a motor of the type referred to.

Still further objects, advantages, and salient features will become apparent from the description to follow, the appended claims, and the accompanying drawing, in which:

FIG. 1 is a broken away side elevation of a missile employing the subject of the invention,

FIG. 2 is an enlarged section taken on line 2-2, FIG. 1, and

FIG. 3 is a section taken on line 3--3, FIG. 2.

Referring now to the drawing, and first to FIG. 1, missile 10 may be of any conventional form which is rotated about its longitudinal axis A to spin stabilize it along its trajectory. The rotation may be effected by any means known in the art, such as by canted vanes (not shown) disposed within a thrust nozzle 12, as disclosed in U.S. Pat. No. 3,017,748 to Burnside, or by a nozzle plate having a plurality of canted nozzles as disclosed in U.S. Pat. No. 2,661,692 to Vegren. As illustrated, however, a rotating band 14 is employed which engages the rifling of a gun barrel, imparting high spin to the missile during its passage along the barrel. To increase the length of the trajectory, a cylindrical solid end burning rocket propellant grain 16 is illustrated which is initiated at a desired time: along the trajectory to supplement the initial thrust imparted to the missile. As will be undetstood, if the rotation is also effected by the propellant grain then a suitable canted nozzle, as above referred to, may be employed. It will be apparent therefore, that the invention is not concerned with the specific manner in which the missile is rotated about its axis but rather with the general criteria that a solid end burning propellant grain is employed which is bodily spinning about its longitudinal axis as it is being consumed along its length.

It will now be assumed that nozzle 12 is of conventional divergent type which produces longitudinal thrust and that the missile is spinning at a high rate and the exhaust gases formed in combustion chamber 18, behind the grain, exhaust directly into such nozzle. Under such conditions, and without use of the present invention, the end surface of the grain burns nonuniformly, burning more rapidly :at its center than at radial outward portions thus producing a central generally conical cavity in the grain which is undesirable, as previously referred to.

The subject of the invention, to now be described, comprises a baffle device 20 interposed between the grain and an exhaust nozzle or nozzles which causes the grain to burn along its end surface in substantially uniform manner. Such device comprises a graphite baffle plate or manifold 22, having a plurality ofangularly spaced radial extending ports 24, communicating at their outer ends with the combustion chamber through ports 26, which as shown, are disposed parallel to axis A. The inner ends of port 26 terminate at a central port 28 in a phenolic base disc 30, which is affixed to plate 22 in any suitable manner.

Since the construction described produced results in which the coning or cratering of the end of the grain was eliminated, it appears that any vortex action adjacen't the grain was reduced sufficiently to eliminate erosive effects which were observed with the former single central exhaust port. It also appears from considerations of conservation of angular momentum that while a vortex action should occur between the end of the grain and the ultimate exhaust port, that the graphite material employed for the baffle or manifold had the physical characteristics to withstand any erosive action.

Obviously many modifications and variations of the present invention are possible in the light of the above teachingsslt is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a spin stabilized rocket motor of the type having a central propulsion nozzle and a cylindrical end burning solid propellant grain, the burning end surface of which forms the front end wall of a cylindrical combustion chamber andwhich is subject to non-uniform consumption across said end surface, tending toform a central crater therein, when the motor and grain are spinning about the axis of the motor above certain spin speeds, the improvements in combination, comprising:

a. means for exhausting gas from said combustion chamber in such manner to minimize the nonuniform buming of said end surface and obviate the formation of said central crater,

said means comprising a baffle member disposed between the nozzle and grain, forming the rear end wall of the combustion chamber, and having a plurality of radially inwardly extending passageways therein,

. the outer ends of said passageways being an'g'ulariy disposed at spaced discrete positions concentric with the axis of the motor for receiving a plurality of gas streams from the combustion chamber,

. the inner ends of said passageways being disposed concentric with the axis of the motor and exhausting into a space ahead of 'the nozzle for joinder of said gasstreams and delivery thereof to said nozzle..

2. Apparatus in accordance with claim 1 wherein said passageways are circular in cross-section. 

1. In a spin stabilized rocket motor of the type having a central propulsion nozzle and a cylindrical end burning solid propellant grain, the burning end surface of which forms the front end wall of a cylindrical combustion chamber and which is subject to non-uniform consumption across said end surface, tending to form a central crater therein, when the motor and grain are spinning about the axis of the motor above certain spin speeds, the improvements in combination, comprising: a. means for exhausting gas from said combustion chamber in such manner to minimize the non-uniform burning of said end surface and obviate the formation of said central crater, b. said means comprising a baffle member disposed between the nozzle and grain, forming the rear end wall of the combustion chamber, and having a plurality of radially inwardly extending passageways therein, c. the outer ends of said passageways being angularly disposed at spaced discrete positions concentric with the axis of the motor for receiving a plurality of gas streams from the combustion chamber, d. the inner ends of said passageways being disposed concentric with the axis of the motor and exhausting into a space ahead of the nozzle for joinder of said gas streams and delivery thereof to said nozzle.
 2. Apparatus in accordance with claim 1 wherein said passageways are circular in cross-section. 